I have parts etc to either set up my latest fixie as a 42x13 or 52x16 which both yield approximatley the same "gear inches". Is there any benefit to one over the other?

larger drivetrain takes slightly longer to wear but is slightly heavier. plus you need to roll your pants higher.

for me it's a wash, whatever's available.

If you are a big and/or strong shifting some mechanical advantage behind the chain can greatly increase drivetrain life.

it'll make you look right 'ard mate.

Wait, I think I get what you're saying, but come at it again?

OP: when you push 85 gear inches, you can ride whatever you want. I would go with the 42 setup unless the 52 chainring is something pretty quality if we're talking about the same crank.

Larger chainrings: look cooler(?), longer drive train life, slightly "smoother" feeling due to increased chain wrap

Also, a smaller chainring will give greater acceleration.

The same gear ratios will give a similar top speed, but you will get there quicker with a small chainring

You must have strong legs whichever one you choose. 85 gear inches is a bit much for me going up hills.

I run 52, what they said about the reduced wear is true in my experience. You're probably already aware but you may have to worry about clearing the chainstays with bigger chainrings. You might need to factor in your bb spindel's length in terms of suitability.
I notice you're going fixie, but another benefit with 52 is that you're in a better place to work with most easily available SS freewheel sizes (such as shimano in 16, 17, 18t) if you decide to go SS freewheel at a more challenging gear ratio. With a 42T chainring, those common sizes would be too easy.

Giventhe same gear ratio...that makes no sense.

Well, at least theoretically, it's true: smaller sprocket and chainring = less moment of inertia (rotational mass)

less moment of inertia means faster acceleration at equal pedaling force.



I, personally, wouldn't be able to notice that small a difference in momen of inertia, but, yeah... smaller chainrings and sprockets mean faster acceleration.

Thats why I fill my tubes with helium and run rim less wheels. Makes me accelerate fater!

True, true...but were talking extremely insignificant here. Your chaingring has way less diameter than your wheels and is spinning 2-3 times slower. Wheel mass is WAY more significant. Hell, the weight of your pedals and shoes and crank arm length would even be way more relevant to acceleration than the diameter of your chainring.

Smaller chainring means there is more mechanical advantage between you and the chain which means more force on the chain for the same total mechanical advantage between you and the rear hub. More force = more wear and if you exceed the strength of the chainring(easily possible for a big dide with a 48 even) ridiculous wear.

Don't forget larger chainring = easier to go out of round/easier for cheap chainrings to be out of round

In bmx, everyone started to go with micro gearing. 25-9 even 24-8. The problem is the chain only goes over 3 teeth as opposed to a 11t driver which would go over 4, 16t which would go over 6 or so. When you reduce the amount of surface area on the chain more stress is put on each link, theoretically increasing the amount of stress put on the chain. Kids were snapping chains right and left with 24-8, not to mention the sprockets and drivers wear rediculously fast.

*this is an extreme example*

Absolutely agreed. I think you understand where my post was coming from, anyway.

I, personally, prefere larger chainring + sprocket combos, because the chain AND all the cogs last noticeably longer.
Disclaimer: this is based on my personal observation and experiences, and is my opinion only - I don't mean to be argumentative. If you have reasons to ride 12t sprockets, I will respect your choice.

With larger ring/cog, isn't your chain less likely to jump ship?

Smaller chainring.

1. Lighter (less chain, less ring - negligable savings)
2. 16t and smaller for NJS (haha)
3. You can hop higher curbs or parking wedge things w/o worrying about bashing your chainring.

For real though? I'd choose the better quality ring.

Probably- more chain wrap = more teeth on ring/cog engaged with the chain. Which probably leads to a more secure drivetrain. Chain tension and chainline are way more important in determining if your chain will jump ship.

My guess would be no, because the size of the rings won't matter if the chain tension is stable. I consider chain dropping an issue of chainline/tension, not size of rings.

I wanted to say that a smaller chainring means smaller revolutions which means you'll more often be in a familiar position to hop/skid in an emergency situation... and that's the reason I ride a 42 (this situation applies to me more specifically because I went from 46x15 to 42x15 and noticed the difference immediately). The increase in control of my bike is really comforting and lets me enjoy the ride that much more.

i think you mean fewer gear inches means more revolutions. i believe the op wishes to compare different sized drivetrains with the same gear inches.

you wanted to say it then you realized that it made no difference if the ratio is the same and a larger cog would have the same effect?

The only 'problem' with large chainrings is that if you want to gear down, besides changing to a smaller ring, you've got to use some big a$$ cog.

I was thinking of my own scenario which involved the same cog in my transition...I see that the OP is focusing on gear inches... scold me more, please.